Apparatus for threading an intermediate transfer member of a printing system

ABSTRACT

A printing system is described that has an intermediate transfer member in the form of a seamed endless belt for transporting an ink image from an image forming station, at which an ink image is deposited on the intermediate transfer member, to an impression station, where the ink image is transferred onto a printing substrate. The belt has along its edges formations of a greater thickness than the belt. The formations are received in channels to guide the belt and maintain the belt under lateral tension. Two drive members are provided, each located within a respective one of the channels. The two drive members are connected for movement in synchronism with one another and each has a respective laterally projecting gripper shaped for form locking engagement with the formations on a leading end of a strip from which the intermediate transfer member is to be formed. Rotation of the drive members during installation of a new intermediate transfer member serves to thread the strip through the printing system by pulling the strip from its leading end.

FIELD

The present disclosure relates to a printing system in which liquid inkdroplets are deposited at an image forming station onto a movableintermediate transfer member and transferred at an impression stationfrom the intermediate transfer member onto a printing substrate.Specifically this disclosure pertains to an apparatus for threading theintermediate transfer member through the various stations of theprinting system.

BACKGROUND

The present Applicant has previously disclosed a printing system andprocess wherein images made up of inks having an aqueous carrier arejetted onto a recirculating intermediate transfer member that transportsthem to an impression station where they are transferred to the desiredprinting substrate (e.g., paper, cardboard, plastic films etc.). Asagainst inkjet printers, that deposit ink directly onto the printingsubstrate, such systems allow the distance between the surface of theintermediate transfer member and the inkjet print head to be maintainedconstant and reduces wetting of the substrate, as the inks may be driedwhile being transported by the intermediate transfer member before theyare transferred to the substrate. Consequently, the final image qualityon the substrate is less affected by the physical properties of thesubstrate and benefits from various other advantages as a result of theimage remaining above the substrate surface. More details of such asystem are disclosed in WO2013/132418, filed on Mar. 5, 2013 andincorporated herein by reference.

The present disclosure is concerned with an apparatus for assisting withthe initial installation of the intermediate transfer member in such aprinting system and with its replacement when the need arises withouthaving to separate the various components of the printing system.

At the image forming station, the intermediate transfer member in such aprinting system needs to pass through a narrow gap between the printheads and its own support and drive system, and it needs to bemaintained both taut and at a fixed distance from the print heads. Toachieve this, WO 2013/132418 describes in FIG. 11 how formations may beprovided along the lateral edges of the intermediate transfer memberthat are received in guide channels having, for instance, a C-shapedcross section that is shown in FIG. 12 of the latter publication. Theformations may be the teeth of two zip fastener halves, or any othertype of “beads” that can properly move in the guide channels, that areattached to the respective lateral edges of the intermediate transfermember and their engagement in the guide channels serves both toconstrain the path followed by the intermediate transfer member and tomaintain it under lateral tension.

The intermediate transfer member is seamed once installed and startslife as a long strip, also termed a blanket in practice, but the latterterm will not be used herein as it also common to refer to the installedintermediate transfer member as a blanket. The strip needs to bethreaded through the various stations of the printing systems and, afterit has been threaded around its entire path, its ends strip can be cutto the correct length, if necessary, and joined to one another to form acontinuous loop. The ends of the strip can be attached to one another bysoldering, gluing, taping (e.g., using Kapton® tape, RTV liquidadhesives or PTFE thermoplastic adhesives with a connective stripoverlapping both edges of the strip), or any other method commonlyknown. Any method of joining the ends of the blanket strip to form anintermediate transfer member may cause a discontinuity, referred toherein as a seam.

The seam can be of different types. In particular, the edges may overlapone another or a patch may be applied to overlie the two ends. In eithercase, the seam may be subsequently processed, such as my grinding, toreduce its thickness.

To feed the strip into the printing system, it was proposed by thepresent Applicant in WO2013/136220 to provide entry points in the guidechannels and to mount an external threading mechanism, shown in FIGS. 9and 10 of the latter publication, for gripping the formations on thelateral edges of the strip and advancing its two lateral edges at thesame rate into their respective guides. However, even with the aid ofsuch a threading mechanism, it was found that the intermediate transfermember was difficult to install on account of buckling on meetingresistance or an obstruction.

It was also proposed in WO2013/136220 (see FIG. 13) to provide a loop ofcable permanently housed in one or both of the tracks. The aim was toanchor the leading end of the replacement belt to the cable then to usethe cable to feed the strip through the various tracks. During normaluse, the cable(s) would remain stationary in the track(s) and only berotated during installation of a new intermediate transfer member.

The use of cable loops was not found satisfactory and the presentdisclosure therefore aims to simplify the task of installing andreplacing an intermediate transfer member in an indirect printingsystem.

SUMMARY

According to the present disclosure, there is provided a printing systemhaving an intermediate transfer member in the form of an endless beltfor transporting an ink image from an image forming station, at which anink image is deposited on the intermediate transfer member, to animpression station, where the ink image is transferred onto a printingsubstrate, the belt having along its edges formations of a greaterthickness than the belt, which formations are received in channels toguide the belt and maintain the belt under lateral tension, the printingsystem further comprises two endless drive members, each located withina respective one of the channels, the two drive members being connectedfor movement in synchronism with one another and each having arespective laterally projecting gripper shaped for form lockingengagement with the formations on a leading end of a strip from whichthe intermediate transfer member is to be formed, rotation of the drivemembers during installation of a new intermediate transfer member beingoperative to thread the strip through the printing system by pulling thestrip from its leading end.

The threading mechanism in the present proposal differs from thatdisclosed in FIGS. 9 and 10 of WO2013/136220 in that the strip forforming the intermediate transfer member is pulled through the printingsystem by its leading end instead of being pushed from behind along itsdesired path. The strip is therefore maintained under longitudinaltension and thereby avoids buckling of the strip if the leading end ofthe strip should encounter resistance or an obstruction.

The present disclosure differs from the embodiment shown in FIG. 13 ofWO2013/136220 in that it uses grippers that engage the formations on thestrip. This can ensure that the imaginary line extending the twogrippers lies exactly perpendicular to the longitudinal axis of thestrip, to avoid any tendency for the strip to be pulled towards one sideor the other. Furthermore, because the grippers are capable of engagingwith the formations provided on the lateral edges of the leading end ofthe strip, the strips may to be cut from a continuous web without anyspecial adaptation being required for connection of the strip to thedrive members used to thread it through the printing system.

In some embodiments, the drive members have the form of chains ortoothed belts in place of cables. As these are driven by toothed drivewheels or cogs, slipping can be avoided and this ensures that the stripis always pulled along at exactly the same rate on its two sides.

Despite engagement of the lateral edges of the leading end of the stripin the guide channels, the leading edge of the strip may still sag atthe centreline of the strip and prove hard to introduce into some of thenarrow gaps through which it has to be threaded.

To assist in this task, in some embodiments of the invention, theleading edge of the strip is cut at an angle and is not perpendicular tothe lateral edges of the strip.

A severely inclined leading end would need to be trimmed after it hasbeen threaded through the printing system to avoid increasing the lengthof the unusable seam region of the intermediate transfer member. Tominimise the wastage caused by such trimming while retaining theadvantage of smoother threading, it is convenient to form the leadingedge with a V-shaped cut out with two sections inclined relative to thelateral edges of the strip instead of one extending across the entirewidth of the strip.

After threading of the intermediate transfer member, its ends need to betrimmed to the correct length and joined to one another to form a seam.The seam preferably extends at an angle that is slightly offset from theperpendicular to the lateral edge of the strip. This angle is so thatthe entire width of seam, which may not have the same thickness as theremainder intermediate transfer member, should not pass at the same timeover the drive rollers of the intermediate transfer member and create anabrupt change in tension in the intermediate transfer member. The angleis chosen as a compromise between avoiding such changes in tension andincreasing the length of the unusable seam region.

To assist in forming the seam between the ends of the strip after it hasbeen threaded through the printing system, a support plate may beprovided in the printing system for supporting ends of the strip thatare to be cut and joined to one another, the support plate notcontacting the intermediate transfer member subsequent to installationof the intermediate transfer member.

Alternatively, the leading end of the strip can be transiently attachedto a removable leader. The leader can have lateral formations compatiblewith the grippers of the drive members and can be releasably attached tothe leading end of the strip. While the removable leader may be shapedas above described for the leading end, it may alternatively oradditionally be made of a material less prone to sagging than theintermediate transfer member being installed. The leader can be made ofa material rigid enough to allow threading of the strip through narrowgaps without interfering with adjacent parts of the printing system, butflexible enough to bend within the lateral guide channels, were curvedguide channels be present along the path followed by the intermediatetransfer member. In the following, and unless otherwise clear fromcontext, the term leading end interchangeably refer to the integralleading end of the strip being installed and to the removable leadertransiently attached to this end.

When a removable leader is attached to the strip, the strip may have apredetermined length and its ends may be shaped to enable the belt tohave substantially the same thickness at the seam as along the remainderof its length. This may be achieved by forming a respective rebate inthe rear surface of each end to receive a tape having the same width asthe combined widths of the two rebates and a thickness matching thedepth of the rebates. In this way, the tape used to join the two ends ofthe strip is recessed into the strip instead of lying above it andtherefore does not cause a thickening of the intermediated transfermember at its seam.

In accordance with a second aspect of the disclosure, there is provideda method of installing an intermediate transfer member in a printingsystem having an intermediate transfer member in the form of an endlessbelt for transporting an ink image from an image forming station, atwhich an ink image is deposited on the intermediate transfer member, toan impression station, where the ink image is transferred onto aprinting substrate, the belt having along its edges formations of agreater thickness than the belt, which formations are received inchannels to guide the belt and maintain the belt under lateral tension,which method comprises providing an elongate strip of a length exceedingthe circumference of the intermediate transfer member, connecting aleading end of the strip to two grippers projecting laterally from twodrive members that are each disposed within a respective one of the twochannels by engaging formations on a leading end of the strip with thetwo grippers, rotating the drive members in synchronism with one anotherto thread the leading end of the strip through the stations of theprinting system, and joining the ends of the strip to one another toform an endless intermediate transfer member after the strip has beenthreaded through the printing system.

In an embodiment in which the strip has a separable leader and the endsof the strip are rebated, and joined to one another by adhering a tapewithin the rebates in the ends of the strip to form a seam whilemaintaining the uniformity of the thickness of the intermediate transfermember. By “rebated”, it is meant that the thickness of the ends of thestrip is reduced, such as by grinding, so as to define a recess forreceiving the tape when the two ends of the strip are abutted againstone another.

In accordance with a third aspect of the disclosure, there is provided aprinting system having an intermediate transfer member in the form of anendless belt for transporting an ink image from an image formingstation, at which an ink image is deposited on the intermediate transfermember, to an impression station, where the ink image is transferredonto a printing substrate, the belt having along its edges formations ofa greater thickness than the belt, which formations are received inchannels to guide the belt and maintain the belt under lateral tension,the printing system further comprising two endless drive members, eachlocated within a respective one of the channels, the two drive membersbeing connected for movement in synchronism with one another androtation of the drive members during installation of a new intermediatetransfer member being operative to thread a strip from which theintermediate transfer member is to be formed through the printing systemby pulling the strip from its leading end, wherein opposite ends of thestrip are formed with rebates for receiving a joining tape to form aseam, and are joined at a seam while maintaining the thickness of theintermediate transfer member uniform throughout its length

In accordance with a fourth aspect of the disclosure, there is provideda method of installing an intermediate transfer member in a printingsystem having an intermediate transfer member in the form of an endlessbelt for transporting an ink image from an image forming station, atwhich an ink image is deposited on the intermediate transfer member, toan impression station, where the ink image is transferred onto aprinting substrate, which method comprises providing an elongate stripof predetermined length corresponding to the circumferential length ofthe intermediate transfer member, threading the strip through theprinting system, providing rebates along the end edges, and joining theend edges to one another by means of tape that is recessed within therebates and secured to the ends of the strip, so to form a seam havingsubstantially the same thickness as the strip.

The end edges of the strip may be rebated prior to threading of thestrip through the printing system and a leader may be releasably securedto one of the two rebated ends of the strip to assist in threading thestrip through the printing system.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described further, by way of example, withreference to the accompanying drawings, in which:

FIG. 1 is a section through a support system of an intermediate transfermember;

FIG. 2 is a perspective view of one end of the support system shown inFIG. 1;

FIG. 3 is a section through one of the guide channels of theintermediate transfer member with one of the drive members runningalongside the formations on the lateral edges of the intermediatetransfer member;

FIG. 4 is a detail of FIG. 3 drawn to an enlarged scale;

FIG. 5 shows the leading end of a strip that is threaded through aprinting system to form an intermediate transfer member; and

FIG. 6 shows the manner in which the ends of a strip may be joined at aseam while maintaining the thickness of the intermediate transfer memberuniform throughout its length.

It will be appreciated that for simplicity and clarity of illustration,elements shown in the figures have not necessarily been drawn to scale.For example, the dimensions of some of the elements may be exaggeratedrelative to other elements for clarity. Further, where consideredappropriate, reference numerals may be repeated among the figures toindicate identical components but may not be referenced in thedescription of all figures.

DETAILED DESCRIPTION OF THE DRAWINGS

An intermediate transfer member support system 10 shown in FIGS. 1 and 2comprises two lateral frames 12 and 14, arranged one on each side of theintermediate transfer member 18, and various support, drive andtensioning rollers 16 extending transversely between the two frames 12and 14 to constrain the intermediate transfer member to follow a closedloop and pass through the various stations of the printing system. Theremainder of the printing system and more details of the intermediatetransfer member support system are well documented in the prior art andneed not therefore be repeated in the present context. Essentially, inthe region designated 20 the intermediate transfer member passes beneathan image forming station where ink is deposited on the intermediatetransfer member to form an image. The intermediate transfer memberrotates clockwise as viewed to carry the ink image to the regiondesignated 22, where the wet image is heated to evaporate the inkcarrier and leave behind a tacky resin film. Along its lower run, theintermediate transfer member passes through one or more impressionstations where it is pressed against a substrate, so that the tacky filmseparates from the intermediate transfer member and is transferred tothe surface substrate.

The intermediate transfer member support system 10 is designed to ensurethat the intermediate transfer member remains substantially flat andtaut as it passes the regions 20 and 22 and as it approaches the nip ofthe impression stations. In order to achieve this objective, the edgesof the intermediate transfer member 18 have formations 30 in the form ofzipper teeth, shown in FIGS. 3 and 4, that have a greater thickness thanthe transfer member 18 and are received in C-shaped guide channels 32secured to the lateral frames 12 and 14. The guide channels 32 are shownin FIG. 1 and their position in the support system is shown in FIG. 2.Further details of the formations 30 and the guide channels 32 aredisclosed WO2013/132418 and are shown in FIGS. 11 and 12 of thatpublication. It is to be understood that the guide channels may have anyalternative cross section shape, as long as the lateral formations andthe guide channels are compatible and suitable to guide the intermediatetransfer member and maintain it under lateral tension while the printingsystem is operating.

The intermediate transfer member 18 is installed by threading a strip18′ through the printing system and connecting its ends to one anotherby means of a seam, in order to form a seamed endless loop. The presentdisclosure is concerned with simplifying this task, which needs to becarried out, not only during manufacture, but from time to time duringuse as the intermediate transfer member is subjected to wear.

The installation of a new or replacement intermediate transfer member 18is made difficult by the fact that its lateral formations 30 need to beintroduced into the guide channels 32 and, as can be seen in FIG. 1,these need not be continuous. Because they maintain the intermediatetransfer member under lateral tension, engagement of the formations 30in the guide channels 32 creates drag and makes threading of the strip18′ from which the intermediate transfer member more difficult.

To mitigate this problem, in the disclosed embodiment, two endless drivemembers, in the form of chains 50 passing over sprockets 52 are providedalongside the edges of the intermediate transfer member 18, preferablywithin the enclosed cross section of the C-shaped channels 32. Referenceto chains passing over sprockets is intended herein to include theequivalent of toothed belts passing over toothed pulleys. Each of thechains 50 has a respective laterally projecting gripper 54, most clearlyshown in FIG. 4, that engages the formations 30 of the intermediatetransfer member strip 18′ at its leading end in a form locking manner.After the gripper 54 has engaged the formations on the leading edge ofthe strip 18′, the two endless chains 50 are driven to pull the strip18′ by its leading end, in the direction shown by the arrows in FIG. 3,through the various stations of the printing system. To ensure that thetwo chains 50 move in synchronism, two of their drive sprockets 52 aremounted on a common axle that is connected either to a crank for manualoperation, or to a suitable motor if threading is automated.

The intermediate transfer member 18 may in some locations have to bethreaded through a gap that is as narrow as 2 mm, while its width maytypically be about 1,000 mm. Sagging of the leading edge of the strip18′ being threaded through the printing system can therefore cause aproblem. This is mitigated by forming a V-shaped cut-out 60 in theleading edge of the strip in the manner shown in FIG. 5.

Once the strip has been pulled around the entire printing system, andits leading end comes round to the end of the support system shown inFIG. 2, the opposite ends of the strip are laid over a support plate 62and joined to one another to form a seam, which may, as shown in FIG. 5,extend along an inclined line 64. After the seam has been formed, atension roller is extended to maintain the intermediate transfer memberunder the desired longitudinal tension and space it from the grippers 54that remain stationary during operation of the printing system.

To form the seam, the two ends of the strip 18′ may be laid one over theother on the support plate 62 and cut along the inclined line 64. Whileretained on the support plate 62 with the cut edges in abuttingrelation, an adhesive tape may be laid over the two ends to create thedesired join. Such a method of forming the two ends results in a seamhaving an increased thickness and in order that it should not create asudden change in tension as it passes over drive rollers or through animpression station, the cut line 64 may be inclined in the mannerillustrated in FIG. 5.

It is alternatively possible to form a seam without increasing thethickness of the intermediate transfer member and this is shown in FIG.6. In this case, the strip 18′ is made to a predetermined length and isattached to a separable leader at its leading end. The leading 19 andtrailing 21 ends of the strip 18′ proper, would be ground down to formrebates 70 for receiving a tape 75 that is as wide as the two rebates72. The tape 72 is secured to the two ends of the strip 18′ by a layer74 of adhesive.

In an embodiment where the thickness of the strip 18′ is about 550 μm,the rebates in the ends of the strip may have a depth of 200 μm. Therebates can then accommodate a tape having a thickness of about 150 μmleaving 50 μm for the thickness of the adhesive layer 74.

The separable leader should be made of a flexible material so that itmay follow the path of the intermediate transfer member but it may bemade of a stiffer material than the strip 18′ so as to have lesstendency to sag. The leader may, as shown in FIG. 5, have a V-shapedleading edge and it should have formations that are continuous with theformations on the sides of the strip 18′.

It is understood that in addition to the image forming station and theimpression station above-mentioned, a printing system may furthercomprise a treatment station and/or a cleaning station to respectivelytreat and/or clean the intermediate transfer member, a drying station toevaporate liquid carrier out of the ink image, a cooling or a heatingstation to modify the temperature of the intermediate transfer memberalong its path, a finishing station for further processing the printedsubstrate, and so on. All such stations need not be considered in detailin the present context.

It is appreciated that certain features of the invention, which are, forclarity, described in the context of separate embodiments, may also beprovided in combination in a single embodiment. Conversely, variousfeatures of the invention, which are, for brevity, described in thecontext of a single embodiment, may also be provided separately or inany suitable sub-combination or as suitable in any other describedembodiment of the invention. Certain features described in the contextof various embodiments are not to be considered essential features ofthose embodiments, unless the embodiment is inoperative without thoseelements.

Although the present disclosure has been described with respect tovarious specific embodiments presented thereof for the sake ofillustration only, such specifically disclosed embodiments should not beconsidered limiting. Many other alternatives, modifications andvariations of such embodiments will occur to those skilled in the artbased upon Applicant's disclosure herein. Accordingly, it is intended toembrace all such alternatives, modifications and variations and to bebound only by the spirit and scope of the appended claims and any changewhich come within their meaning and range of equivalency.

In the description and claims of the present disclosure, each of theverbs “comprise”, “include” and “have”, and conjugates thereof, are usedto indicate that the object or objects of the verb are not necessarily acomplete listing of features, members, steps, components, elements orparts of the subject or subjects of the verb.

As used herein, the singular form “a”, “an” and “the” include pluralreferences and mean “at least one” or “one or more” unless the contextclearly dictates otherwise.

Unless otherwise stated, the use of the expression “and/or” between thelast two members of a list of options for selection indicates that aselection of one or more of the listed options is appropriate and may bemade.

Unless otherwise stated, adjectives such as “substantially” and “about”that modify a condition or relationship characteristic of a feature orfeatures of an embodiment of the present technology, are to beunderstood to mean that the condition or characteristic is defined towithin tolerances that are acceptable for operation of the embodimentfor an application for which it is intended.

To the extent necessary to understand or complete the presentdisclosure, all publications, patents, and patent applications mentionedherein, including in particular the applications of the Applicant, areexpressly incorporated by reference in their entirety by reference as isfully set forth herein.

1-18. (canceled)
 19. An intermediate transfer member (ITM) for aprinting system, the ITM comprising an endless belt formed by threadingan elongate strip through the printing system and joining the twoopposing ends of the strip at a seam, the elongate strip comprising: a.a leading edge, such that when the strip is threaded through theprinting system it is pulled from the leading edge; and b. lateralformations provided along the edges of the strip, and adapted to bereceived in channels of the printing system so as to guide the strip andmaintain it under lateral tension when driven by two drive membershaving respective laterally projecting grippers shaped for form-lockingengagement with the lateral formations on the leading end, wherein thetwo ends of the strip are formed with rebates for receiving a joiningtape to form a seam, and are configured to be joined at a seam whilemaintaining the thickness of the intermediate transfer member uniformthroughout the length of the seam.
 20. The intermediate transfer memberof claim 19, wherein the leading edge is V-shaped.
 21. The intermediatetransfer member of claim 19, wherein the leading edge is formed as partof a leader that is separably connected to one end of the strip.
 22. Theintermediate transfer member of claim 19, operable to transport an inkimage from an image forming station at which the ink image is depositedon the ITM, to an impression station where the ink image is transferredonto a printing substrate.
 23. The intermediate transfer member of claim19, wherein the lateral formations have a greater thickness than that ofthe strip.
 24. A method of forming an intermediate transfer member (ITM)for use in a printing system from an elongate strip having lateralformations provided along the edges thereof, the method comprising: a.connecting a leading end of the strip to two grippers projectinglaterally from respective drive members disposed within respectivechannels of the printing system, the grippers being shaped forform-locking engagement with the lateral formations; b. rotating thedrive members in synchronism with one another to thread the leading endof the strip through a plurality of stations of the printing system,such that the lateral formations are received in the channels so as toguide the strip and maintain it under lateral tension; and c. joiningthe ends of the strip to one another to form an endless belt after thestrip has been threaded through the printing system, wherein: i. theends of the strip are rebated, and ii. the joining comprises adhering atape within the rebates in the ends of the strip to form a seam whilemaintaining the uniformity of the thickness of the intermediate transfermember.
 25. The method of claim 24, wherein the leading edge is formedas part of a leader that is separably connected to one end of the strip.26. The method of claim 25, additionally comprising the step ofseparating the leader from the remainder of the strip before thejoining.
 27. The method of claim 24, wherein the leading edge isV-shaped.
 28. The method of claim 24, wherein the lateral formationshave a greater thickness than that of the strip.